1. Field of the Invention
The present invention relates to a method for immediate and high-precision detection of impurities which contaminate raw pulp slurry during raw pulp processing, as well as an apparatus therefor.
2. Description of the Related Art
Pulp used in paper making is subject to contamination by impurities such as dirt, pitch, or ink or toner residue. These impurities cause trouble during the paper making process and their contamination lowers the quality of the product. Control of impurities is therefore necessary during the raw pulp processing. Usually, the raw material is periodically sampled to prepare a hand-made sheet, and the production process is controlled by the operator's visual determining of the contaminating impurities. The present applicant has already proposed a dirt measuring device using hand-made sheets (Japanese Patent Application No. 4-117668). There have also been developed an on-line measuring device for use during raw material processing (Japanese Unexamined Patent Publication No. 63-295946) and a method for measuring slurry pulp (Japanese Unexamined Patent Publication No. 61-272639).
Although the above-mentioned dirt measuring device using hand-made sheets provides highly precise measurements, time is required to prepare the hand-made sheets, leading to increased risk of damage to the sheets because of the delay for control during the raw material processing. On the other hand, in the case of the on-line measuring device used during the raw material processing, the setting location is limited to being on the drum-washer filter, and the poor condition of the measuring surface of the raw pulp on the drum-washer filter produces a crude measuring limit, making it impossible to obtain a satisfactory resolution. Furthermore, in the method for measuring slurry pulp, it is necessary to prepare a constant predetermined-dilution raw pulp concentration and flow rate for the measurement, and thus time is required for pretreatment prior to the measurement.